Catalytic alkylation of isoparaffins



Patented Oct. 3, 1944 UNITED 2,359,542 ICE CATALYTIC ALKYLATION F ISOPARAFFINS William E. Bradley, Los Angeles, and Karl J. Korpi, Rcdondo Beach, Calif., assignors to Union Oil Compan of California, Los Angeles, Calif., a corporation of California No Drawing. Application July 1, 1940,

Serial No. 343,432

6 Claims.

The present invention relates to the manufacture of paraifinic hydrocarbons of a branched chain structure particularly suitable for use as fuel in automobile and aviation engines, and is a continuation in part of our application, Serial Number 204,354, filed April 26, 1938. More specifically, the invention includes a process for combining certain isoparafiinic hydrocarbons with olefinic hydrocarbons to produce branched chain parafilnic hydrocarbons of relatively higher molecular weight, these products of reaction being particularly suitable as a motor fuel, or as a, constituent thereof, in that these hydrocarbons possess unusual anti-detonating characteristics. The invention further includes the use of special catalysts and conditions of operation for the manufacture or synthesis of the described valuable compounds.

Owing to the adoption of high compression ratios, both in automobile and aviation engines, the petroleum industry has resorted to the use of cracking operations as a general means of producing motor fuels of high anti-knock value. These cracking operations, however, produce, as a by-product, undesirably large losses, as for example, in the formation of gases containing considerable proportions of olefins. In one of its embodiments, the present process is directed to the eflicient utilization of the lower molecular weight or normally gaseous olefinic hydrocarbons and of certain paraffinic hydrocarbons present in commercial gas mixtures to produce high antiknock hydrocarbon fractions suitable for use as motor fuels.

Aside from the olefins present in the gases formed as a by-product of the petroleum cracking operations, olefinic hydrocarbons occur along with paraflinic and other saturated hydrocarbons produced by gas making processes, as well as byproducts in various chemical industries. Also, olefinic hydrocarbons are obtained by a simple dehydrogenation of the corresponding paraffinic hydrocarbons. In general, olefinic hydrocarbons are relatively more chemically active than other classes of hydrocarbons. Thus, even under comparatively mild catalytic influences, the olefinic hydrocarbons exhibit a high reactivity in their tendency to polymerize and to form substances of higher molecular weight. On the other hand, parafiim'c hydrocarbons, as for example, isobutane, isopentane, etc., normally occurring in natural gas or any similar or related hydrocarbon fractions, are usually considered to be more or less chemically unreactive.

It has previously been discovered that certain isoparafiinic hydrocarbons, and particularly the relatively low molecular weight isoparaffinic hydrocarbons, may be caused to react with olefinic hydrocarbons to form valuable derivatives there- '01, The reaction between one or more olefinic molecules and an isoparaffinic hydrocarbon molecule produces an alkylated or branched chain paraflinic molecule. This product is hereinafter termed an. alkylate in order to distinguish it from a polymer? which is the product resulting from the interaction of two or more olefinic molecules. Theoretically, the reaction between the isoparaffinic hydrocarbon and an olefin, in the presence of a suitable alkylating catalyst, is of a simple character. Thus, the combination-which takes place when isobutane is chemically combined with a butene may be expressed by the following equation:

(3 4H) Isobutane 04118 CsHre Butene Octane The above equation shows the union of one molecule of isobutane with one molecule of a butene to produce one molecule of a branched chain octane. Similar reaction equations may be written for the alkylation of the above or other isoparaffins with various olefins. As will be brought out more fully hereinbelow, the term alkylation includes not only the simple chemical combination ofthe isoparafiinic molecules with the olefinic molecules introduced into the sphere of reaction, but also the production of branched chain paraffinic hydrocarbons having a molecular weight less than that obtainable by the simple chemical addition of one isoparafiinic molecule to one olefinic molecule introduced into the reaction sphere.

Olefins, as stated above, when subjected to proper reaction temperatures and pressures, in the presence of a suitable catalyst, such as sulfuric acid, tend to form polymers. In fact, this tendency to polymerize, at least under certain conditions, occurs in preference to alkylation so that if a mixture of isoparaffin or even cyclic hydrocarbons and olefins is brought into contact with. sulfuric acid, the reaction products will be found to contain only a relatively small percentage ofalkylated products ofjreaction, the greater proportion of the olefins, and particularly the more reactiveolefins, having polymerized to produce unsaturated polymers in preference to their addition to the isoparailinic or cyclic hydrocarbons. 1

It is, therefore, the main object of the-present invention to provide a process wherein alkylation of the isoparaffins by olefins shall be favored in preference to the polymerization of .the olefins introduced into the reaction zone for the purpose of combining with the isoparafiinic hydrocarbons. 7

It is a further object of the invention to provid a process wherein valuable motor fuelfracmally liquid olefins preferably having not more than about twelve carbon atoms in the, molecule. It is a still further object to provide a process of the type described wherein the alkylation reaction is favored, and wherein substantially no pol ymerization of the olefins occurs.

It has now been discovered that the above and other objects may be attained by conducting the reaction between the isoparafiinic hydrocarbons and olefins in the presence of a catalyst mixture comprising sulfuric acid and an acid or an oxide of an element of the fifth group of the periodic system, such as for example an oxide of phosphorus. It has also been discovered that relatively. high boiling hydrocarbons within the gasoline boiling range, and having high anti-detonating characteristics may be produced by efiecting" a reaction between isoparaffinic and olefinic hydrocarbons in the presence of a catalyst consisting of phosphoric and sulfuric acids.

The term isoparafiins or isoparaflinic hydrocarbons, as employed in the present specification and claims, relates to the lower members, namely, isobutane, isopentane and isohexane. It has been discovered that the rates of alkylation of these 'isoparaffinic hydrocarbons, maintaining other conditions equal, are not the same. Thus, the rate of alkylate formation when isopentane is employed is considerably slower than the rate of alkylation of isobutane, while the alkylation rate of isohexane is even still lower.

As to the terms olefins and olefinic hydrocarbons, as usedherein, they relateto both the normally gaseous olefins, which comprise the hydrocarbons between about propylene and pentenes, and the normally liquid olefins, such as. the hexenes and the higherolefins. It is to be noted, however, that it is not desirable to employ very high boiling olefins since the alkylation reactions become unfavorable when such olefins are employed. It has been found that, when normally liquid olefins are to be employed, it is preferable, although not absolutely essential, to use fractions having not more than about twelve carbon atoms per molecule. 7 7

It is to be understood that the reference to isoparafiinic and olefinic hydrocarbons includes the use of these hydrocarbons individually, or in mixtures with other hydrocarbons of the particular class, as well as mixtures thereof with other hydrocarbons.

Recently considerable, attention has been paid to the alkylation of aromatic and related com pounds by means of low boiling olefinic, hydrocarbons or olefin-containing gases in the presence of a catalyst consisting of commercial sirupy phosphoric acid, i. e., orthophosphoric acid. Sim

, ilarly, it has recently been discovered that mixtures of phosphoric and sulfuric acids are suitable catalysts for the alkylation of aromatic hydrocarbons with olefins. It is known, however, that catalysts suitable for the alkylation of aromatic hydrocarbons do. not always prove to be efiicient or suitable in the catalytic alkylation of isoparaffinic hydrocarbons. Thus, for'example, under conditions comparable to those employed in the catalytic alkylation of aromatic hydrocarbons, commercial sirupy phosphoric acids have been found to be completely unsuitable for the alkylation of the. isoparaflinic hydrocarbons with olefins. The reaction product formed during this treatment with ortho-phosphoric acid contained substantially no alkylates, the products instead consisting essentially of olefin polymers. Theseresults indicate that although orthoephosphoric acid is capable of catalyzing the addition of olefins to aromatic hydrocarbons, it is not effective as a catalyst in causing the addition of isoparaffinic hydrocarbons to olefins.

It has also been previously discovered that strong sulfuric acid, such as for example, sulfuric acid having a 98% H2804 content, is capable of catalyzing the addition of olefinic hydrocarbonsto isoparaflinic hydro-carbons. However, sulfuric acids of this high strength tend'to a certain degree to react with the hydrocarbons. Thus, the use of strong sulfuric acid causes some side reactions which form sulfur dioxide, carbonization products and water. Thes products progressively lower and finally completely inhibit the catalytic activity of the acid catalyst em.. ployed.

It has now been discovered that the use of mixtures of sulfuric and phosphoric acids, as catalysts for the alkylation of isoparaffinic hydrocarbons of the typeof isobutane, isopentane and isohexane, with olefinic hydro carbons re sults in higher yields, of alkylates and a longer catalyst life as compared to the alkylation reaction in which the sulfuric acid alone was employed. This discovery is unexpectedin view of the above described apparent inability of phosphoric acid, when used alone to catalyze the addition of the olefins to the isoparaflins.

reacting isoparafl'inic hydrocarbons of the type of isobutane, isopentane. and isohexane, with normally gaseous or normally liquid olefinic hydrocarbons, or withboth types of olefins, in the presence of a catalyst comprising a mixture of sulfuric acid and of acids or oxides of phosphorus, thereby producing high yields'of saturated alkylates boiling within the gasoline.

The invention still further resides; in, reaeting isoparafiinic hydrocarbons, having less, than seven carbon atoms per molecule, with oleiinichydro carbons of more than two and less than thirteen carbon atomsv per molecule, in, the presence of a catalyst comprising amixtureof phosphoric and sulfuric acids in substantialproportions,

whereby high yields of products, of reaction areproduced, these products ofv reaction predominating in saturated branched chain alkylates boiling within the gasoline range and being substantially free from polymers. The invention also includes the step of conducting the above reaction at approximately atmospheric. temperatures, i. e., at about 70 to 7,5 F15 in one of its preferred embodiments, the invention also includes the realization of the reaction substantially in the liquid phase. Therefore, when the reaction is realizedv at the above temperaturesin the neighborhoodv of 75 F., it is frequently. es sential, or at least advisable, to employ pressures which are slightly superatmospheric, these being used to maintain the hydrocarbon fractions in a liquid state. U

The invention also includes, reacting the lower molecular weight isoparaiiinsg. or thd, type of isobutaneto isohexane with. olefins of above two and below about thirteen carbon atoms per The invention may, therefore, be stated to reside in molecule, at substantially atmospheric temperatures and at pressures sufficient to maintain the hydrocarbons substantially in a liquid state, in the presence of a catalyst comprising a mixture of phosphoric and sulfuric acids. Thus; a mixture consisting of volumes of commercial sirupy phosphoric acid (86% to 90% aqueous solution of ortho-phosp-horic acid) and 90 volumes of commercial 98% sulfuric acid, was found to give excellent yields of alkylates within the gasoline boiling range, these alkymers being substantially free from products of olefin polymerization.

The reason for the unexpected eifect of added phosphoric acid on the catalytic activity of the sulfuric acid for the alkylation reaction is not clearly understood at the present time. However, it is possible that, because of the affinity of phosphoric acid for olefins and the known fact that at room temperature phosphoric acid acids of phosphorus which may be employed in connection with sulfuric acid to produce the mixed catalyst suitable for alkylation of the specified isoparaffins with the olefins:

Hypophosphorous acid, H3PO2 Orthophosphorous acid, H3PO3..P2O3.3H2O Pyrophosphorous acid, H4P2O5..P2O3.2H2O Hypophosphoric acid, H4P206..P204.2H2o Metaphosphoric acid, HPO3..P2O5.H2O Tetraphosphoric acid, HsP4O13..P2O5.1 /2H2O Pyrophosphoric acid, H4P2O1..P2O5.2H2O Orthophosphoric acid, H3PO4..P2O5.3H2O

Of those listed, the use of some of these acids, such as orthophosphoric, pyrophosphoric and tetraphosphoric acid is now believed to be preferable, these being usable alternatively in different mixtures though without identically equivalent results.

The following examples are presented to show the advantages obtainable when using a mixture of sulfuric acid and a phosphoricacid as a catalyst in place of sulfuric acid alone. In these experiments, the isoparafiinic fraction employed comprised a narrow cut obtained from the stabilization of natural gasoline, and an analysis of this fraction indicated that it consisted of approximately 85% isobutane and normal butane. It is obvious, however, that the isoparaflinic fraction to be alkylated according to the present invention may consist of hydrocarbons other than isobutane such as, for example, isopentane, or may comprise a mixture containing these and other isoparaflins.

The specific olefin-containing fraction ;employed was derived from petroleum cracking operations, and had substantially the following composition:

It is thus seen that the above olefin-containing gases contained about 49.0% unsaturates, exclusive of ethylene, the ratio of propylene to the butylene being about 1:1.

Two runs were made: In one of these the catalyst consisted of sulfuric acid having a 98% H2804 content, while in the second run a mixture consisting of 10% by volume of 85% orthophosphoric acid and of 90% by volume of 98% sulfuric acid was used as the catalyst. In each case the reaction was continued for eight hours at a temperature of 75 F. and at a pressure of between 40 and 70 pounds per square inch gauge. The procedure used in both cases was as follows: About 1800 grams of the above described isobutane-containing fraction were first commingled with 1500 milliliters of the given catalyst, and about 2000 grams (or about 3600 milliliters) of the olefin-containing fraction were then gradually conveyed to the reaction zone, the rate of olefin addition being about 3.0 milliliters per minute. During the reaction the mixture was maintained in a state of violent agitation. After all of the olefin stock had been added, agitation was discontinued and the two phases allowed to separate. The hydrocarbon phase was then separately withdrawn and stabilized to remove the fractions boiling below the gasoline range. This was obtained by distilling the hydrocarbon phase under pressure to a temperature of about to F. and a pressure of 15 pounds absolute in the reflux column. The residual fraction comprised the fraction predomiating in alkylates within the gasoline boiling range.

In the experiment in which 98% sulfuric acid alone was employed as the catalyst the yield of alkylate, based on the amount of olefins present in the charging stock, was 148% by volume. This alkylate contained 1% of olefin by weight. Of this alkylate approximately 83% by volume distilled over at 310 F., the resulting distillate, equivalent to 121.2% by volume of the unsaturates originally charged, having a distillation curve which showed that this fraction was suitable as an aviation motor fuel. The knock rating of this fraction, as determined by the A. S. T.'M. method was 88.5. Similarly, the yield of alkylate from the experiment in which phosphoric acidsulfuric acid mixture was employed was 154.4% by volume, said alkylate containing only 0.3% by weight of olefins. About 88.5% of this alkylate distilled over at 310. F. The resulting distillate, equivalent to a yield of 136.6% by volume based on the olefin charged, had a knock rating of 90.0, and was also suitable as motor fuel for aviation engines.

The above runs clearly disclose the advantages of employing a mixture of phosphoric and sulfuric acids as against using sulfuric acid alone. Thus, the phosphoric acid-sulfuric acid mixture allowed the realization of approximately 15% more of aviation gasoline of 1.5 points higher knock rating than was obtained by the use of sulfuric acid alone.

When the reaction is efiected in the liquid phase, it is preferable to maintain, during the whole course of the reaction, a concentration of isoparafiins in excess of that quantity theoretically necessary to combine with the olefins. Thus, in the preferred embodiments, the isoparaffins, such as isobutane, isopentane, isohexane, or mixtures thereof, are first commingled with the above described catalyst, and the olefins are then slowly and gradually introduced into the isoparafiln-catalyst mixture. The presisoparafiinic molecules.

ence of an excess of isoparaffins and the relatively slow and gradual addition of the olefins is necessary to prevent any local over concentration of the olefins which would favor polymerization instead of the alkylation of the isoparafiins. In other words, the constant presence of an excess of isoparaffinic molecules increases thechances of an immediate or substantially immediate contact of an activated olefin with an activated isoparaffin molecule. Simultaneously, the relatively slow addition of the olefins decreases their concentration, thus also increasing the possibilities of the alkylation reaction: totake place in preference to the polymerization. of the olefins.

The above disclosure is presented in connection with the alkylation ofisoparaffins with olefins and emphasizes the simple addition of the relatively low molecular weight normally gaseous olefins to the specified isoparaffins. In addition it-was discovered that in reacting the isoparaffins with normally liquid olefinic hydrocarbons the reaction product comprised a large propor-- tion of saturated hydrocarbons. of" branched chain structure eboiling substantially within the gasoline range, Such hydrocarbons evidently could be formed by an initial scission of at least one of the original reacting hydrocarbons into two or more hydrocarbons of lower molecular weight, and the subsequent reaction of these lower molecular weight hydrocarbons to produce Or, this may be the result of'simple addition of the introduced olefinic molecule to the isoparaffinic molecule followed by scission of the product. Specifically, this alkylation reaction might be termed cracking alkylation in order to distinguish it from the straight or simple addition of an olefin to an isoparafiin as already described hereinabove. The cracking alkylation reaction, therefore, may be described as including the step of reacting olefin molecules with isoparaffin molecules to produce one or more paraffinicalkylates which have molecular weightsof less than that which would [be obtained providing the reaction were one of simple addition in which one olefinic molecule reacts with one iso-paraffinic molecule to produce a brached chain saturated molecule having a molecular weight equal to the sum of the 'molecular weights. of the reacting olefin and isoparafiin.

Therefore, it has also-been discovered that the reaction between the isoparaflins and certain of the olefins (and particularly the normally liquid olefins) in the presence of the described-catalyst comprising strong sulfuric acid and an acid or oxide of phosphorus, may result in both the simple alkylationof the isoparafiins by theolefins added, and in the cracking alkylation' in which, as stated, alkylates are produced which havea lower molecular weight than would be-- obtained by simple addition of an isoparaffin-to an olefin; The, higher molecular weight olefins, as-olefins above about clodecenes, however, appear to be unsuitable to react effectively with the isoparaffins v or end point of around 425 F. The term atmospheric pressure refers to pressures in the neighborhood of 760 In. In. of mercury, while atmospheric temperature and room temperatune relate to temperatures in the vicinity of 70 F. to F.

In carrying out the present invention the apparatus used and the conditions of operationchosen in respect to temperature, pressure, proportions of reacting constituents, etc., may be varied to suit individual cases. Although the alkylation reactions described herein were realized at substantially room temperature, under certain conditions lower or higher temperatures may be employed. Furthermore, the rate and manner of adding the olefin may be altered. Also, the foregoing is not to be construed as limiting the present invention to the use of orthophosphoric acid alone. Thus, as brought out above, other acids of phosphorus, such as pyrophosphoric acid and tetraphosphoric acid may be used with equal facility and in proportions higher or lower than the 10% suggested in the above illustration.

As many other pertinent and equally different embodiments may be made by those skilled in the art without departing from the spirit and scope hereof, it is to be understood that there is no intention to be limited by specific embodiments disclosed herein except as defined in the appended claims.

We claim:

1. A process for the production of alkylated high knock-rating gasoline from olefins having more than two and less than thirteen. carbon atoms per, molecule and from isoparaflins-having.

less than seven carbon, atoms per. molecule,.whichcomprises reactingsaid olefins with saidisoparaf fins in the presence of a catalyst comprising a mixture of concentrated sulfuric acid-and an oxide of phosphorus.

2. In a process according to claim 1. wherein the reaction is realized at moderate temperatures and under sufficient pressure to maintain said olefins and isoparaffins in a substantially liquid state. r

3. The process of reacting isoparaffinic hydrocarbons having less than seven carbon atoms per molecule with normally gaseous olefins having more than two carbon atoms per molecule, to produce saturated alkylates boiling within the gasoline range and substantially free from polymers, which comprises reacting said isoparaflinic and olefinic hydrocarbons at moderate temperatures in the presence of a catalyst consisting of concentrated sulfuric acid and an oxide of phosphorus.

4.. In a process according to claim 3, wherein the reaction is realized at a pressure sufficient to maintain the olefins and isoparafiins in a substantially liquid state.

5. A process which comprises alkylating acyclic paramns containing at least one tertiary carbon atom with mono-olefins in the presence of a catalyst comprising at least one oxide of an element of the, fifth group of the. periodic system in concentrated sulfuric acid.

6. A process which comprises alkylating acyclic isoparaffins with mono-olefins in the presence of a catalyst; comprising an: oxide of an element of the fifth group of the periodic system in concentrated sulfuric acid.

WILLIAM E. BRADLEY. KARL J. KORPI. 

